1. Field of the Invention
The present invention relates to an organic light emitting display, and more particularly, to an organic light emitting display having an encapsulation layer with an improved structure and a manufacturing method thereof.
2. Description of the Related Art
Generally, organic light emitting displays include an organic light emitting diode (“OLED”) deposited on a thin film transistor (‘TFT’) of an electric circuit so that a selected emitting layer is emitted in response to a signal controlled by the TFT.
FIG. 1 shows the typical structure of such an organic light emitting display. As described above, an OLED 20, including an anode 21, a light emitting layer 22 and a cathode 23, is deposited on a TFT 10. The TFT 10 includes a substrate 11, a gate electrode 12, a source region 13, a drain region 14 and a via hole 16. Therefore, when a voltage is applied to the gate electrode 12, a current passes through the source region 13 to the drain region 14 via a channel opened in an organic semiconductor region 15. A current flows to the anode 21, the light emitting layer 22 and the cathode 23 through the via hole 16. At this time, in the light emitting layer 22, the action of emitting energy in the form of light occurs as a result of electric coupling, i.e., as a result that the light emitting layer 22 is excited by the recombination of holes and electrons. This light may be a luminous spot corresponding to one pixel of the display panel.
An encapsulation layer 30 protects the light emitting area OLED 20 from moisture and oxygen. As shown in FIG. 2, the encapsulation layer 30 has a multi-layered structure in which an inorganic film 32, such as a ceramic, and an organic film 31, such as a polymer, are alternately deposited. Such a structure is disclosed in U.S. Pat. No. 6,268,695. The organic film 31 can be composed of either of acrylic, methacrylic, polyester, polyethylene terephthalate, polyethylene, or polypropylene, etc. The inorganic film 32 can be composed of one of In2O3, SnO2, ITO (Indium Tin Oxide), SiO2, Al2O3, TiO2, In2O3, SnO2, SiN, SiC, SiON, etc. In this multi-layered structure, the inorganic film 32 prevents the penetration of oxygen and moisture and the organic film 31 provides flexibility.
The total number of layers should be at least 10 to enable the multi-layered structure, in which the organic film 31 and inorganic film 32 are alternately deposited, to properly perform the hermetic sealing and protection functions. That is, as described above, the inorganic film 32 mainly prevents the penetration of oxygen and moisture. If the thickness of the inorganic film 32 is increased, the hermetic sealing protection improves, but the flexibility is drastically decreased. As is well known, the organic light emitting display aims at being as flexible as paper that can be rolled and a decrease in flexibility is a drawback of the article. Therefore, it is preferable to include a plurality of thin inorganic films 32 between the organic films 31 with good flexibility so that the organic light emitting display has both flexibility and hermetic sealing protection. In addition, at least 10 inorganic films have to be deposited to reliably prevent the permeation of moisture and oxygen.
Because many layers have to be deposited, the manufacturing process is very complicated. In particular, since the encapsulation layer 30 is made by laminating at least 10 times, the overall manufacturing process is complicated and productivity is low.